Relay switching circuits



Patented June 2; 1942 UNITED STATES PATENT OFFICE RELAY swrrcnmo omourrsHarold L. Barney, Lconia, N. 1., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation or New YorkApplication 0mm 22, 1940, sens! No. 362,197

(Cl. its-44$ 2 Claims.

The invention relates to switching circuits and particularly to relayswitching circuits controlled by alternating current. 1

The invention is particularly applicable to, although not limited to,voice-operated switching circuits of the syllabic" type, employed intwoway telephone systems, which are responsive to the syllabicvariations in speech waves but are substantially unresponsive tocomparatively steady noise waves. in the prior art disclosed in FisherPatent 1,939,680, issued December 19, 1933, a pair of polarized relaysare connected in reverse order to the output of a low-pass filter, thecut-oil Irequency of which is about 22 cycles. The filter is connectedin the output 01' a push-pull vacuum tube detector circuit the input ofwhich is supplied from a transmission line carrying speech waves andsubject to interfering noise waves.

- One 01' these relays operates upon the initial application of speechwaves to the circuit and the other upon the cessation of the appliedspeech waves, the low-pass filter preventing transmission 01' therelatively steady rectified current due to noise waves to the relays.Other syllabic switching circuits of the prior art, for example, thosedisclosed in Nyquist Patent 1,749,841, issuedMarch 11, 1930, employ aplurality of tandem detector circuits with an intermediate lowpassfilter and selective networks transmitting 3 switching circuits so as toobtain equivalent operation with the employment of less apparatus.

These objects are attained in accordance with the invention by a circuitemploying a single vacuum tube detector and a neutral relay.

The various objects and features of the invention' will be betterunderstood from the following detailed description when read inconjunction with the accompanying drawing in which:

Fig. 1 shows schematically a prior art syllabic switching circuit;

Figs. 2 to 4 show schematically improved syl-' In one circuit of thistype labic switching circuits embodying different modifications oi theinvention; and

Figs. 5 to 8 show curves illustrating the operation of the circuits ofthe invention.

In the syllabic switching circuit or the prior art shown in Fig. 1, thesyllabic detector circuit SD comprising the push-pull vacuum tubedetector DI. and the low-pass filter F having a cutofl. at about 22cycles, has its input connected to a line transmitting speech waves andsubject to interfering noise waves, and its'output coupled through thelow irequency transformer T1 to the operating windings in series of thetwo polarized switching relays TMI and TMF, the biasing windings ofthese two relays being supplied in series with biasing current frombattery 3 through resistance R1, the operation of either relay TMI or'I'MF causing the circuit C to be opened. The current flowing in theoperating windings of the two relays TMI and TMF, corresponding to aspeech input pulse such as illustrated in Fig. 5, would be somewhat asshown in Fig. 6. On increasing amplitudes at the input the currentflowing through the operating winding of the two relays is positive, andon decreasing amplitudes the current flows in the negative direction.Relay TMI is poled to operate on the positive current and relay TMF onthe negative current. Operations of the contacts of these relays for thesingle input pulse are as illustrated in Fig. 7.

The circuit of the invention illustrated in Fig. 2 differs from theprior art circuit shown in Fig. 1 in the substitution of a singledetecting vacuum tube D: for the. push-pull vacuum tube detector D1 inthe latter circuit, and the substitution-eta single neutraP' relay N forthe two polarized relays TMI and TM! 01 the prior art circuit. Theneutral relay N may be any oi. the types known in the prior art, whichby suitable mechanical biasing means provides operation in the samemanner for the positive and negative parts of the applied alternatingcurrent waves. One type of relay providing such operation is disclosedin the United States patent to Gachet, 1,992,610, issued February 26,1935. The current flowing in the operating winding of relay N, eitherpositive or negative, will cause operation of the relay against itsmechanical bias, resulting in contact closures which should be identicalwith those shown on Fig. 7. The low frequency transformer T1 operates tosuppress the direct current component of the detector output currentfrom the winding 01' relay N.

In syllabic switching circuits of the. general ill trated mg. 1employing "two polarre- The single neutral relay N in applicantfs provedcircuit may be readlly'adapted topertorm in the same manner as the twopolar relays of the prior art circuit in this respect simplyby shuntingits operate winding with acopper oxide varistor VAR. as shown in Pig. 3.This varistor may be usedin series with a-resistance Re'to limit itsshunting eilect, as 3, and

either-the initial or final less sensitive.

The circuits oi Figs.1 ,2 and screen shown 'rm and IMF. it is'customaryto make the trated in Fig. Hor the prior jarticircuit employ- V ing: twopolar relays as'shown in Figg-l. Di!- relay 'rur: less sensitive thanthe relay-"i'MILv have been illustrated and} described=topersonsskilledintheart.

with a low frequency transformer T1 used to suppress the direct currentccmponentirom the detector output from the, relaywindings; Fig';;4 3shows a modified circuit arrangement inaccord-fl ance with the inventionwhich uses an auxiliary vacuum tube ior performing "the function or thelow frequency transformer-in the other circuit-- This vacuum tube desinated v1 isused as a direct current amplifier and has a constant directcurrent in its plate} circuit on which are super,-

imposed the variations at'syllabic frequencies,

corresponding to the; output oi the resistancecapacity filter F2 in itsco'ntroitg'rid-cathode circuit, which is connected to the 'outputioithelow,-

pass filter F inthesyllabic detectorcircuit;

The operating (left-hand) winding of the'jneutrai. relay N is includedin the plate-cathode circuit of the direct current amplifier tubeV1-..',I-h e 1 plate current of the tube V1 passi through relay windingfor a single applied'speech pulse would be somewhat as shown in Fig. 8.In,

7 the circuit of Fig. 4, the direct current compo! nent of the platecurrent is balanced out in itseil'ect on the magnetic circuit of relay Nby the current .in .the (right-hand) biasing winding leaving the relayarmature to be held in the unoperated position by the mechanical bias.Thus,

when'the plate current of tube V1 increases above its nominal value,relay N will operate with a.

positive value oi total magnetic flux induced by i'erent sensitivitiesof the initial andiinaioperations'oi' the relay N may beeasily obtainedin the circuit of Fill.v 14 by. increasing "or d the value oi thent'by.."su it i the "1 8 -Operating windings.

Various "modifications-oi the circuits w spirit snd'scopefoi theinventiwil Whatis claimedis:-

fl -in combination, asyllablc; detector aving= an inputcircuit supp iedwith speech and an cutput circuit. a singlegneutr'al. relay-hav jvinglan operating winding coupledtosaid-outputi; circuit, means for.suppressing the Ldi-rect,; cur.-' 'f,- rent componentof thesyllablefdetector 'output. ."current from said winding, said relaybeing'oper- Y I atively responsive in thesar'ne directionto the positiveand negative'portions of the syllable cu'rrent in said detector-outputcircuit and -'a-circuit' including a unilateral device and an impedanceoi suitable 'value shunted across saidoperating winding to make'theoperation of said reiayless 2. In combination, a syliabic detectorhaving an input circuit supplied with speech. currents, a direct currentamplifier comprising an electron discharge device having an inputcircuit con nected to the output or said syllabic detector and an.output'circuit, a' neutral relay having a magnetic core and an operatingwinding which is' connected in the output circuit of said elec- 'l 'trondischarge. device, said relay being opera-.-

tively responsivevin the same direction to the positive and negativeportions of the syllabic cur-'- rent in the output circuit of saiddevice, and meansto prevent the direct current component of the currentin the output circuit of said device from appreciably affecting theoperation of said relay comprising another winding on said relaysupplied with biasing direct current, operating to substantially balanceout the flux in said core induced by said direct current componentflowing through said operating winding.

HAROLD L. BARNEY.

